(1) An example of a conventional robot hand will be described. FIG. 15 shows a thumb of a robot hand having five fingers like a human hand. The robot hand has a thumb, an index finger, a middle finger, a ring finger, a little finger, and a palm. The thumb shown in FIG. 15 includes a first joint 107 that bends forward, a second joint 108 that turns inward and outward, a third joint 109 that bends forward, a fourth joint 110 that bends forward, a first motor 111, a second motor 112, a third motor 113, a fourth motor 114, a first motor encoder 115, a second motor encoder 116, a third motor encoder 117, a fourth motor encoder 118, an asymmetric differential speed reducer 119, a joint axis integral speed reducer 120, a worm reducer 121, and a 6-axis force/moment sensor 122.
Here, the rotation amounts of the motors 111 to 114 can be detected by the motor encoders 115 to 118 directly connected to the motor shafts. The axes of the joints 107, 109, and 110 are parallel to each other, and the joint axis of the joint 107 and the joint axis of the joint 108 cross each other at one point at right angles. The first motor 111 and the second motor 112 are overlapped and fixed to the palm.
The thumb shown in FIG. 15 moves as follows. By the fourth motor 114, the joint axis of the joint 110 axially rotated by 90 degrees with respect to the motor shaft can be driven via the worm reducer 121. By the third motor 113, the joint axis of the joint 109 rotated by 90 degrees with respect to the motor shaft can be driven via the joint axis integral speed reducer 129. The asymmetric differential speed reducer 119 is configured as a mechanism in which the shaft of a third bevel gear (not shown) is formed to be hollow and the shaft of a fourth bevel gear (not shown) is made to penetrate through the third bevel gear to allow the second joint 108 to rotate around its axis and the first joint 107 to rotate around its axis.
Here, when the first motor 111 and the second motor 112 rotate the same angle in directions opposite to each other, the finger rotates around the axis of the second joint 108 via the bevel gears inside the asymmetric differential speed reducer 119. When the first motor 111 is fixed and the second motor 112 is rotated, the finger rotates around the axis of the first joint 107. By adopting the asymmetric differential speed reducer 119, the rotation angle around the axis of the first joint 107 can be made larger, and the joint axis can be provided at a position close to the surface side of the palm, so that movement similar to the movement of a human hand is realized in external appearance (Patent Document 1).
(2) Another example of a conventional robot hand will be described with reference to FIG. 16. The robot hand shown in FIG. 16 drives and rotates a drive shaft 821 (not shown) by a motor 822 to swing a finger 814a with respect to a palm 812 (not shown) in an extended state (dotted line in the drawing) of the finger 814a where joint sections 816 to 818 straighten. When the drive shaft 821 is thus driven and rotated, the joint axis 820 accordingly swings around the intersection with the drive shaft 821, and as a result, the finger 814a swings with respect to the palm 812.
On the other hand, in order to bend the finger 814 from the extended state, a bevel gear 844 is driven and rotated by a motor 834. When the bevel gear 844 is thus driven, the rotational driving torque thereof is transmitted to the proximal section 816 via the bevel gear 828 and the bevel gear 824, and as a result, the proximal section 816 turns around the joint axis 820, and the finger 814a tilts toward the inner side of the hand. In this case, the bevel gear 844 is driven and rotated according to driving of a bevel gear 838 (not shown) to rotate a link 846 (bevel gear 826). Specifically, as described above, the proximal section 816 and the intermediate section 817 of the finger 814a are linked to each other by the link 848, so that when only the proximal section 816 is attempted to be turned around the joint axis 820, this turning is obstructed by the link 848. Therefore, in order to avoid this, a cam 846 is turned as shown by the arrow in the same drawing according to the turning amount (angle) of the proximal section 816. In detail, a pulley 838 (not shown) is driven and rotated by a motor 832. When the pulley 838 is thus driven, the rotational driving torque thereof is transmitted to the bevel gear 826 via a bevel gear 830 (not shown), and as a result, the link 846 integrally fitted to the bevel gear 826 is turned.
The above-described movement is when the finger 814a bends to the inner side of the hand with respect to the palm 812 while the finger 814a is in an extended state, and on the other hand, when the finger 814a bends from a middle point, the link 846 (bevel gear 826) is further rotated from the above-described position. When the cam 846 is thus rotated, the intermediate section 817 is drawn to the inner side of the hand via the link 848, and as a result, the intermediate section 817 turns around the joint axis 819a, and the intermediate section 817 bends to the inner side of the hand with respect to the proximal section 816. When the intermediate section 817 thus bends with respect to the proximal section 816, the distal section 818 is drawn via a link 850, and as a result, the distal section 818 turns around the joint axis 819b, and the distal section 818 bends to the inner side of the hand with respect to the intermediate section 817.
Here, a movement of bending the entire finger 814a around the joint axis 820 with respect to the palm 812 and a movement of bending the intermediate section 817 and the proximal section 816 around the joint axes 819a and 819b are described separately, however, by performing these movements concurrently, a movement of bending the finger 814a can be performed smoothly. By performing a movement inverse to the above-described movement, the finger 814a can be returned to an extended state (Patent Document 2).    [Patent document 1] Japanese Patent No. 3245095    [Patent document 2] Japanese Unexamined Patent Publication No. JP2005-66803